休息 leaves the door open: you pause now and return later. 摆烂 closes it. The speaker has stopped protecting the outcome and is willing to let a task, plan, or situation remain bad rather than spend more effort repairing it.
That surrender is why the word often arrives with a laugh or a shrug. Said about yourself, it can turn frustration into self-mockery; said about someone else, it can sound like a judgment that they have abandoned responsibility.